In recent years, a dramatic increase in storage capacity of recording media such as hard disks is demanded. In response to such demands, development of magnetic recording media having high storage capacities is under way.
In a magnetic recording medium used in current hard disks, a fixed region of a thin film containing polycrystalline substance of magnetic substance particles is recorded as one bit. To increase the recording capacity of a recording medium, it is necessary to increase the recording density. That is, a recording mark size that can be used for recording per bit needs to be made smaller. However, if the recording mark size is simply made smaller, it becomes impossible to ignore the influence of noise depending on the shape of magnetic substance particles. If the particle size of magnetic substance particles is made smaller to reduce noise, it becomes impossible to keep a record at ordinary temperature due to thermal decay.
To avoid such problems, various patterned media including a bit patterned medium (BPM) that record/read a single magnetic dot as a single recording cell by dividing a recording material by a non-recording material in advance are proposed.
According to a conventional method of producing a patterned medium, a mask having a master pattern equivalent to a desired magnetic pattern is produced on a medium and after the pattern being transferred to a magnetic recording layer, peeling, that is lift-off, of the mask to maintain the smoothness of the surface. Lift-off layers provided in a mask include, for example, a metal layer of Cr, Mo and the like and an organic layer of a resist and the like.
In a patterned medium working process, it is desirable to make the lift-off layer as thin as possible because the lift-off layer is not needed for other processes than peeling. However, if the lift-off layer is thin, peeling defects are more likely to occur when the mask is peeled. For example, peeling is not sufficient in outermost and innermost circumferential regions without any pattern because the surface area of an exposed portion on a side surface to be a penetration location of a peeling liquid is narrow. This also applies to a servo pattern. If a mask peeling defect occurs, a mask of a height of a few tens to 100 nm remains as a protrusion on the medium, making floatability of a head when mounted on a drive worse.